How is a CO2 storage site monitored?

Monitoring will play an important role during the injection phase of a CO2 storage project, both for the purpose of assuring worker and public safety and confirming that the storage project is performing as expected. If the seal of a storage formation or the plug in an abandoned well is going to fail, this will mostly likely occur during the injection phase when the pressure in the storage formation is highest. After injection stops, monitoring is also likely to continue for observing the post-injection pressure decline and to monitor continued movement, if any, of the injected CO2. The frequency and intensity of monitoring will decrease over time as greater assurance of long-term storage integrity is obtained. If repeated measurements indicate that the CO2 is not moving and remains trapped in the storage formation, there may come a time when monitoring is no longer needed. The timeframe over which this occurs could be as short as a few years in a depleted gas reservoir with a well-defined geologic trap. For storage in a saline formation without a closed trap, more time may be needed before a combination of capillary trapping and solubility trapping (dissolution of CO2 in the salt water) eventually immobilize the CO2. Information from model studies and ongoing monitoring would be used to assess how much longer monitoring should continue. For storage in oil fields, which like gas reservoirs have time-tested geologic seals, the duration of post-injection monitoring is likely to be shorter than for saline formations. In December 2010, the U.S. Environmental Protection Agency (EPA) finalized rules for CO2 injections that require a 50-year post-closure monitoring period for CO2 injection projects.

Project field site for testing CO2 storage in a depleted oil reservoir near Hobbs, New Mexico. In this case, injection into the subject reservoir will be through an inactive well, while a producing well and two shutoff wells are used for monitoring.

There is a large portfolio of technologies available for monitoring of storage projects, many of which are highly developed due to decades of experience in other applications such as the oil and gas industry, and natural gas storage. For more information, NETL’s “Monitoring, Verification, and Accounting of CO2 Stored in Deep Geologic Formations” BPM provides an overview of MVA techniques that are currently in use or are being developed; summarizes the U.S. Department of Energy’s (DOE) Monitoring, Verification, and Accounting (MVA) R&D Program; and presents information that can be used by regulatory organizations, project developers, and national and State policymakers to ensure the safety and efficacy of carbon storage projects.

Myth:

It is impossible to adequately monitor CO2 injection sites.

Reality:

Extensive monitoring of CO2 injection sites is already taking place both at the surface and in the subsurface. This is an important regulatory requirement for these projects to operate in the United States.